2-Chloro-5-chloromethyl-1,3-thiazole (hereinafter, abbreviated as CCT in some cases) is an important compound as an intermediate for producing biologically active compounds such as pesticides (see Patent Literature 1: JP-A No. 3-157308). As a typical method for preparing CCT, there has been a known method of reacting 2-chloroallyl isothiocyanate with a chlorinating agent (see Patent Literature 2: JP-A No. 4-234864). For purifying crude CCT prepared by the said method, the following methods have previously been known.
The above Patent Literature 2 has described a method of simply distilling under reduced pressure without performing a pretreatment for decomposing impurities present. The method requires attentions in terms of equipment and time, based on the necessity of setting a ref lux ratio to obtain CCT in high purity, because the impurities are azeotropic with CCT. In other words, there is a problem of difficulty to suppress the content of azeotropic impurities present, when the distillation is performed under the whole distilling conditions without a reflux ratio. There is an additional problem that the azeotropic impurities have relatively high melting point and thus are condensed within a distillation equipment system, and the condensed impurities fixed in the equipment piping promote corrosion on the equipment, when the distillation is performed under the whole distilling conditions without a reflux ratio. Whereas, a problem arises that even when setting a reflux ratio to suppress contamination of the impurities, the period of distillation is prolonged, and distillation recovery of CCT is decreased due to low thermal stability of CCT. This tendency is naturally stronger with more increased charge per batch.
To solve the problems of the above purification method, Patent Literature 3 (JP-A No. 9-316062) has proposed a method of recrystallizing crude CCT using an organic solvent. This method, however, requires a large amount of solvent for crystallization, resulting in an expensive material cost. Further, the method requires equipments such as filters for crystal separation and filtration processing, resulting in an expensive cost of equipments. Moreover, since the resultant crystal has a melting point of 30° C., the method requires an equipment for controlling a filtration temperature during the separation of the crystal after the crystallization, resulting in a further cost of equipments and complicated processing operation. In addition, since the resultant crystal has harmful properties such as bad odor, and eye or skin irritation, it is undesirable to use a filter requiring a periodical maintenance such as replacing work of a filter fabric. Therefore, it is hard to say that the purification method by recrystallization is a really excellent one for industrial purification.
Under such a situation as described above, there is a need for a method of purifying CCT, which is less expensive, has good operability, and can recover CCT in high purity and high recovery.